An injured passenger talks on the phone after several subway cars derailed in Moscow on July 15. / AFP

by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

At least 19 people have died and scores more have been injured after a rush-hour subway train derailed in Moscow on Tuesday, health officials said.

Some 150 people were injured, many of them hospitalized, Russian news agency ITAR-TASS said, quoting Moscow's health department chief, Georgy Golukhov. Around 50 people are in grave condition, he said.

The crash is said to have occurred after several cars left a track in a tunnel after a power surge triggered an alarm.

Photos on social media showed passengers walking along the tracks inside the dimly lit tunnel.

There have been 13 emergency incidents on Moscow's metro system so far this year but no one was injured in the earlier incidents, according to ITAR-TASS. Moscow's transit system has been targeted by terrorists in the past but Russian officials Tuesday dismissed terrorism as a possible cause.

Moscow's metro system is one of the world's oldest and most extensive.